The present invention relates to a partial dental prosthesis, and, more particularly, to a partial dental prosthesis which does not cause natural teeth adjacent to the partial dental prosthesis to be damaged and can be stably and steadily supported on an alveolus ridge of the patient.
In FIG. 11 and FIG. 12, which are a plan view showing a typical conventional partial dental prosthesis used widely and a sectional view taken along a line E--E in FIG. 11, respectively, the partial dental prosthesis 1 comprises artificial teeth 2; a denture base 3 holding the artificial teeth 2; wire type clasps 4 provided at both ends of the denture base 3; and a part of an attachment 6 being formed at a side portion of the artificial tooth 2 facing to a side portion of the natural tooth 9 at which the other part of the attachment 6 is formed. At the side portion of the artificial tooth 2, the attachment 6 has a metallic ball 5, a spring 7 urging the ball 5 from the side portion of the artificial tooth 2 toward the side portion of the natural tooth 9 of the patient and a metallic casing 8 in which the ball 5 and the spring 7 are contained. Further, at the side portion of the natural tooth 9, the attachment 6 has a circular concave 10 in which the surface of the ball 5 is partially received when the ball bearing 5 is urged by the spring 7. Numeral 11 indicates an alveolus ridge on which the partial dental prosthesis 1 is supported. The partial dental prosthesis is supported on the alveolus ridge 11 by urging the ball 5 to the circular concave 10 with the spring 7 and by anchoring to the natural teeth 9 with the wire type clasp 4.
In the above described partial dental prosthesis 1, there are several problems, as follows:
(1) The force applied to the natural tooth by the wire type clasp is not always uniform, since the wire type clasp is made of metal which tends to apply a large localized force to the natural tooth. Accordingly, the life span of the natural tooth to be clasped are shortened.
(2) Due to the repeated use of the partial dental prosthesis in the mouth, the wire type clasp is plastically deformed. Therefore, the fixing function of the wire type clasp is reduced. As a result, the partial dental prosthsis supported on the alveolus ridge becomes unstable and unsteady. In that case, it is necessary to correct the shape of the wire type clasp to the original shape;
(3) The wire type clasp is usually provided at a portion where one can see from outside. Accordingly, such an appearence is not preferable from an aesthetic point of view;
(4) The wire type clasp made of metal causes a patient to unpleasantly feel it as an extraneous substance;
(5) The attachment is weak in strength, and insufficient in durability, since the attachment 6 is assembled from very small elements;
(6) The cost of the attachment is high, since the attachment has to be manufactured by precise and fine technique;
(7) The attachment has a problem concerning sanitation, since saliva, dregs in the mouth, and the like are easily stayed in the metallic casing and it is much difficult to clean the interior of the metallic casing.
An object of the invention is to provide a partial dental prosthesis which does not cause natural teeth adjacent to the partial dental prosthesis to be damaged and can be stably and steadily supported on an alveolus ridge of the patient.